------------------
- userId: int
- username: String
- password: String
- role: String
+ login()
+ logout()
- studentId: int
- name: String
+ enrollSubject()
+ dropSubject()
+ retakeSubject()
- advisorId: int
+ approveEnrollment()
- enrollmentId: int
- semester: int
- status: String
+ submitEnrollment()
+ updateStatus()
- staffId: int
+ createPackageEnrollment()
+ determineSchedule()
+ determineLecturer()
+ determineQuota()
- subjectCode: String
- credit: int
+ getCredit(): int
- classId: int
- className: String
- quota: int
+ checkQuota()
- lecturerId: int
by bry